1. Field of the Invention
The present invention relates to a color cathode ray tube (CRT), and more particularly, to an electron gun mounted in a neck portion of a CRT, for exciting a phosphor layer.
2. Description of the Related Art
In general, CRTs are employed in projectors, oscilloscopes, monitors, TV receivers and the like, and an example of a CRT is shown in FIG. 1.
As shown, the CRT includes a bulb 10 having a screen 12 with a phosphor layer 11, and an electron gun 20 sealed in a neck portion 13 of the bulb 10. A deflection yoke 15 for deflecting an electron beam emitted from the electron gun 20 is installed in a cone portion 14 of the bulb 10. Here, the bulb 10 may be formed by sealing a panel and a funnel together. Also, a shadow mask frame assembly may be mounted inside the panel.
There are a variety of electron guns that are sealed into the neck portion according to the type of CRT, that is, either a monochrome CRT or a color CRT, the alignment of electrodes, and the states of voltages applied to various electrodes. One exemplary CRT, as disclosed in U.S. Pat. No. 4,904,898, is illustrated in FIG. 2.
As shown, an electron gun 20 includes a cathode 21 for emitting thermal electrons, a control electrode 22, a screen electrode 23, upper and lower focusing electrodes 24 and 25 separately installed adjacent to the screen electrode 23, and a final accelerating electrode 26 surrounding the end of the upper focusing electrode 25. The cathode 21 and the respective electrodes 22-26 constituting the electron gun 20 are supported by a pair of bead glasses 27 at a predetermined gap.
The electrodes 22-26 are assembled by the bead glasses 27 as follows. First, a spacer is inserted between adjacent electrodes using an assembling set (not shown) to support the electrodes 22-26 in a state in which an electronic lens is formed by application of a voltage. In this state, the bead glasses 27 are heated to a half-melted state. When the heating of the bead glasses 27 is completed in the above-described manner, the heated bead glasses 27 are pressed at either side of the electron gun 20 so that buried portions 28 of the respective electrodes 22-26 are embedded in the bead glasses 27 and cooled.
However, the above-described assembling method in which the respective electrodes 22-26 are fixed to the bead glasses 27, has several problems in that off-axis electrode alignment may occur and a distance variation between electrodes may be increased due to fabrication tolerance of a spacer used for maintaining a constant gap between adjacent electrodes or deformation occurring when the heated bead glasses 27 are cooled.
In particular, the cathode 21, the control electrode 22 and the screen electrode 23, forming a triode of the electron gun 20, sensitively affect the characteristics of the electron gun. Due to the above-stated distance variation or off-axis electrode alignment, enhanced focusing characteristics of the electron gun cannot be attained. Thus, conventionally, in order to detect inferior of electron gun products, the alignment of all electron guns has been examined. However, since the conventional examination method requires many operational processes, it is not possible to enhance productivity.
To solve the above problems, it is an object of the present invention to provide an electron gun for a cathode ray tube, which can improve focusing characteristics by solving distance variation between a cathode and electrodes forming a triode of the electron gun and enhancing the alignment of electrodes.
It is another object of the present invention to provide an electron gun for a cathode ray tube, which can reduce electrode deformation due to a pressing force of bead glasses when electrodes forming a triode are fixed to the bead glasses.
To accomplish the first object of the present invention, there is provided an electron gun for a cathode ray tube including a cathode assembly, a control electrode and a screen electrode installed adjacently to the cathode assembly, and combined so as to be spaced a predetermined gap apart from each other by a gap maintaining means, a plurality of focusing electrodes sequentially installed from the screen electrode, to form an auxiliary lens and a main lens, and bead glasses into which buried portions of the cathode assembly and the respective electrodes are embedded to be supported.
In the present invention, the gap maintaining means which maintains the gap between the two electrodes, may be formed by adhering a ceramic member to the electrodes. In the case where the screen electrode and the control electrode are combined, the buried portions may be installed only at one side of either the control electrode or the screen electrode.